In recent data centers and high-performance computers, communication wiring has been changed into optical wiring to increase transmission rates and transmission capacity, from the need for processing a huge amount of information. Particularly, there are increasing demands for replacing interconnection of short-haul intervals like a CPU-CPU interval, which has been electrical wiring heretofore, with optical wiring. In this regard, the MCF is expected to be applied to the optical wiring, as transmission media capable of providing a plurality of transmission channels at high density and in space-saving design. The MCF has a plurality of cores. For this reason, when connectors are arranged at the ends of the MCF, high-accuracy rotational alignment of the MCF (to rotate the MCF in the circumferential direction around the longitudinal direction of the MCF) is required in order to set array positions of the cores to predetermined array positions.
Patent Literature 1 discloses the technology of processing the MCF so as to have a noncircular cross section with a flat portion formed in a part of the outer peripheral surface, and rotationally aligning the MCF by use of the flat portion. As a commonly-known technology there is the technology of grasping the MCF by means of a grasp rotation jig from one side of the connector and rotationally aligning the grasped MCF while observing the end face of the MCF from the other side of the connector.